Ok, just replaced all the standing rigging. What is the minimum rig tension % I should use before taking her out for fine tuning ? Deck stepped. Masthead Rig. double spreaders 10 mm HS/BS. 8 mm shrouds.
Here is some info on rig tension: The following table gives recommended initial tension settings for 1 x 19 wire rope. It should be noted that optimal rig tension will be a function of the boat design, the rig and the cut of the sails. Headings are: wire diameter, wire breaking strength, forestay tension, shroud tension.
2.5mm 550 kg 80 kg 55 kg
3.0mm 950 kg 145 kg 110 kg
4.0mm 1500 kg 230 kg 160 kg
5.0mm 2000kg 340 kg 230 kg
5.5mm 2800 kg 450 kg 320 kg
6.0mm 3700 kg 590 kg 390 kg
7.0mm 4500 kg 680 kg 450 kg
Forestay tension – masthead rig: It is almost always advantageous to set the forestay tension as high as possible within the limits of structural strength. Generally, it is possible to use 15% of the breaking strain of the wire as the forestay tension. The backstay should be adjusted to maintain a straight mast with the desired forestay tension. The backstay tension will be less than the forestay tension because the backstay makes a greater angle to the mast than does the forestay.
Note that rollerfurling jib tension can only be set by adjusting backstay tension.
Forestay tension – fractional rig: Because the forestay tension cannot be directly balanced by the backstay tension some mast bend is accepted and the sails are cut to accommodate it. Forestay tension of at least 15% of the wire strength is desirable but, if this results in excessive mast bend, it may be necessary to back off the tension.
Upper and lower shroud tension – masthead rig: The initial rig tension should be high enough that the leeward shrouds do not go slack when sailing close-hauled in a brisk breeze. The proper tension for your boat can be found by a few test runs under sail and then a tension gauge can be used to record and maintain this value.
For many boats a shroud tension of 10% to 12% of the wire strength is adequate. In some rigs it may be advantageous to carry a bit more tension in the uppers than the lowers.
Upper and lower shroud tension – fractional rig: In most cases the same comments apply as for masthead rigs. However, there is one exception. Where the upper and lower shrouds on a fractional rig lead to chainplates located aft of the mast – swept back spreaders – most of the forestay tension is balanced by the upper shrouds. A shroud tension as high as 20% of the wire strength may be required to achieve the desired forestay tension. Never exceed 25% of the wire breaking strength.
This information is mainly from Loos & Co, makers of the Loos Tension Gauge. They are located near you in Naples, Florida.
You use a Loos Tension Gauge. There are actually three sizes covering wire diameters from 2.5mm up, but two cover most recreational boat wire sizes: The standard guages are the type A(91M) for 2.5mm to 4mm wire and the type B(90M) for 5mm to 7mm wire. There is a larger size for bigger wire. There is also a Pro range, slightly more accurate and a bit more expensive. Chandlers sell tham for £40 to £60. Search on eBay for a better deal.
Ok. did my playing and set everthing around 15% . Stick up straight, new furler installed no major sag in luff sections. Guess what, 3 hours later all down to 12%.+/- This was as the temprature was falling. New rigging stretching? Using my neighbours Loos Pro, Good bit of kit. How long should I continue to monitor tension before sea trials?
I have a fractional rig (folkboat) and noticed the other day that the lower shroud rigging wires are much looser than the upper shroud wires. And by loose I mean not under much tension. Clearly this is Not Good. Bottlescrew base does not turn easily (if at all) so I've hit with WD40 and will have a shot at tightening tomorrow - at least to a 'by-feel' level of tightness before attmepting to gauge it. Sound sensible/desirable??
How does the gauge work in practice, does it fit 'in-line' and then have to be removed, or does it clamp on the cable recording its tension. Of great interest to me as I may be removing mast later this year to use French canals.